UN inspectors have arrived in Iran to visit a mountainside nuclear facility kept secret for at least three years.

They are to examine the unfinished uranium enrichment site near the holy city of Qom to establish if it is being used for peaceful means.

Iran only revealed last month that the Fordo facility existed, raising international suspicion over the extent and aim of Tehran’s nuclear program.

But Iran says that by reporting the existence of the site voluntarily to the UN’s nuclear watchdog, it “pre-empted a conspiracy” by the US and its allies who may have presented the site as evidence of a secret nuclear program.

The country insists its nuclear program serves to generate power and denies allegations it is trying to make nuclear weapons.